1. Field of the Invention
The present invention relates to a fixing device, and more particularly to a fixing device of an image forming apparatus, in which heat is focused on a position where a heat roller and a pressure roller engage with each other, thereby shortening a warming-up time of the heat roller and enhancing a fixing efficiency.
2. Description of the Related Art
Generally, an image forming apparatus such as a printer, a copying machine, and a composite machine transfers a toner image developed on a photo-sensitive medium onto a paper using an image transfer roller and then, heats and compresses the toner image while passing the paper through a fixing device, thereby fixing the image onto the paper toner.
A conventional fixing device includes a heat roller 51 and a press roller 61 as shown in FIG. 1.
Typically, the pressure roller 61 includes a silicon rubber 63, within which a shaft 62 made of stainless steel is fitted.
A halogen lamp 58 is provided within the heat roller 51, and an aluminum pipe 56 is used as a supporting pipe because of its high heat conductivity, low price, and good machineability. The aluminum pipe 56 is formed with a Teflon-coated toner release layer 52 on its external surface and formed with a light-to-heat converting layer 54 to absorb a radiation energy emitted from the halogen lamp 58 on an internal surface of the converting layer 54.
The conventional fixing device operates as follows.
When electric power is applied, the lamp 58 is lighted and emits the radiation energy. The emitted radiation energy arrives at the light-to-heat converting surface 54 provided on the internal surface of the aluminum pipe 56 and is converted into heat energy, thereby increasing a temperature of an entire area of the aluminum pipe 56.
The heated aluminum pipe 56 transfers heat to the surface of the heat roller 51, and the paper moves in a direction indicated by an arrow 67 and the heat roller 51 and the pressure roller 61 heat and compress the paper when the paper passes between the heat roller 51 and the pressure roller 61, thereby fixing a toner image 66 on the paper.
The conventional fixing device of the image forming apparatus has a problem in that the fixing device requires a long warming-up time for copying or printing because an entire area of the aluminum pipe 56 should be heated.
In particular, a low-speed laser printer set (10–14 ppm), which uses a halogen lamp with a capacity of 500–600 watts and an aluminum pipe with a diameter of 15–20 mm, usually requires a warming-up time of 35–40 seconds and even requires 2–3 minutes for printing free of a fixation problem under a low temperature and a low moisture circumstance, at which heat radiation efficiency is low.
Furthermore, the conventional fixing device, which requires a long warming-up time, has a disadvantage in that the fixing device has a high energy consumption because it has to be supplied with electric power in order to continuously maintain a predetermined temperature during a stand-by mode for a subsequent rapid printing.